1. Technical Field
This invention relates to fuser and pressure roller-type fixing apparatus for fixing images in electrostatographic reproduction machines. More particularly, this invention relates to a wicking device for applying image release liquid to the surface of a roller of such a fixing apparatus.
2. Background Art
Fuser and pressure roller-type fixing apparatus are well known for fusing and fixing toner images on suitable receiver sheets in electrostatographic copiers and printers. Usually, the fuser roller of such a fixing apparatus is heated, and is mounted in rotatable nip-forming contact with a pressure roller. Receiver sheets carrying unfused toner images are passed through the formed nip such that the toner images directly contact the fuser roller. A common problem associated with such fixing apparatus is an undesirable offsetting of the toner making up images being fixed from the receiver sheets onto the surface of the fuser roller.
The toner offsetting to the fuser roller can undesirably transfer to subsequent copies or images being fixed, and to the backside of such copies by way of a nip-forming pressure roller.
In order to prevent such offsetting of the toner images, it is known to apply an image-release liquid, such as silicone oil, to the surface of the fuser roller. As disclosed for example in U.S. Pat. No. 4,908,670 issued to Sylvain L. Ndebi on Mar. 13, 1990, and U.S. Pat. No. 5,043,768 issued to Susan C. Baruch on Aug. 27, 1991, it is known to use a rotatable wicking device for applying the release liquid or oil to the fuser roller surface.
Typically, such a rotatable wicking device includes a rotatable roller that is made from a porous or capillary material, and a liquid or oil distribution tube that is located inside the porous roller. Oil transported from a container to the distribution tube flows through small holes in the distribution tube to saturate the interior surface of the porous roller. The oil is then "pulled" by capillary action of the porous roller from the interior of the porous roller (through pores) to the exterior surface thereof for application to a fuser roller surface.
Ordinarily, the oil flows as droplets through a number (5 to 20) of the small holes in the distribution tube. The droplets then drop under gravity onto the interior surface of the rotatable porous roller for covering a group of pores therein. Capillary flow is then relied upon to pull and distribute oil from the covered pores to the rest of the porous roller in a circumferential direction as well as in a radial direction of the porous roller.
Unfortunately, however, the dropwise supply of oil is random from the distribution tube to the interior surface of the porous roller. Accordingly, the complete covering or saturation of pores therein (which is necessary for capillary flow) is also random. Capillary flow of oil to the surface of the porous roller will therefore also be random until a steady state saturation of the interior surface is reached. Ordinarily, it may take the fixing apparatus fixing 3000 to 5000 image-bearing substrates or copies before such a steady-state condition is reached. The result until then, of course, is poor oiling of the fuser roller surface with increased possibility of undesirable image offset and copy sheet jams.
Additionally, when the fixing apparatus is stopped and the porous roller is no longer applying release oil to the fuser roller, release oil in the porous roller will gravitationally settle to a bottom or lower side of the porous roller to form a "puddle". Due to gravity and capillary flow, the "puddle" further settles downward through the pores of the lower portion of the porous roller. The result is an overly saturated portion of the porous roller. Subsequently, such an overly saturated portion then undesirably causes non-uniform and heavily oiled streaks on the surface of a fuser roller being oiled. Image-bearing substrates fixed at a fixing apparatus including such a fuser roller are therefore likely to contain oil induced defects.